Serotonergic neuron system in the spinal cord of the gar Lepisosteus oculatus (Lepisosteiformes,Osteichthyes) with special regard to the juxtameningeal serotonergic plexus as a paracrine site

Immunohistochemical and electron microscopic studies were carried out to elucidate the structure of the serotonergic neuron system in the spinal cord of the spotted gar, Lepisosteus oculatus, a nonteleost actinopterygian. Serotonin-immunoreactive (5HT-IR) cell bodies and fibers were widely distributed in the spinal cord, constituting an intrinsic neuron system. This system comprised three anatomical cell groups in different portions of the spinal cord, i.e., the rostromedial cell group, the paired ventrolateral cell groups, and the ventral superficial cell group. The rostromedial cell group included cerebrospinal fluid-contacting neurons with intraventricular processes. The immunostained fibers projecting from all three of these cell groups ran in various directions, mainly ventrally and ventrolaterally, and partly gave rise to a dense plexus at the ventrolateral surface of the spinal cord. Immunoelectron microscopy of the relevant portion demonstrated many varicose fibers containing 5HT-immunopositive vesicles. Conventional electron microscopy of the plexus showed that the constituent varicose fibers were unmyelinated and frequently made a direct contact with the basement membrane contiguous to the leptomeniges (meninx primitiva). There, exocytotic figures of cytoplasmic vesicles were demonstrated, suggesting that 5HT may be secreted, in a paracrine way, into the extraspinal space. This specialized area in the gar spinal cord may be referred to as the juxtameningeal serotonergic plexus.     

5一羟色胺能神经对横断损伤脊髓的再支配-脊髓内移植研究

用成年SD大鼠20只在脊髓的低位胸髓完全横断损伤,分别在1周和1月后,用富含5一羟色胺(5—HT)神经元的胚鼠脑干中缝组织悬液植人损伤尾侧的脊髓内,动物存活2个月,脊髓作5—HT免疫组化观察.结果:(1)胚5-HT能神经元能在成年大鼠脊髓内存活,5-HT纤维大多在灰质中延伸并向靶区分布,(2)损伤后1周移植组的5-HT能神经元存活量,5-HT纤维在宿主脊髓内延伸距离,以及5-HT末梢再分布的密度都优于损伤后1月移植组.     

Serotonergic input to cholinergic neurons in the substantia innominata and nucleus basalis magnocellularis in the rat.

The aim of the present study was to determine, at the light microscopic level, whether the serotonergic fibers originating from the dorsal raphe nucleus (B7), median raphe nucleus (B8) and ventral tegmentum (B9) make putative synaptic contacts with cholinergic neurons of the nucleus basalis magnocellularis and substantia innominata. For this purpose, we utilized: (i) the anterograde transport of Phaseolus vulgaris leucoagglutinin combined with choline acetyltransferase immunohistochemistry; (ii) choline acetyltransferase/tryptophan hydroxylase double immunohistochemistry; and (iii) the FluoroGold retrograde tracer technique combined with tryptophan hydroxylase immunohistochemistry. Following iontophoretic injections of Phaseolus vulgaris leucoagglutinin in the dorsal raphe nucleus, labeling was observed primarily in the ventral aspects of the nucleus basalis magnocellularis and in the intermediate region of the substantia innominata. When Phaseolus vulgaris leucoagglutinin was combined with choline acetyltransferase immunohistochemistry, a close association between the Phaseolus vulgaris leucoagglutinin-positive fibers and cholinergic neurons was observed, even though the majority of the Phaseolus vulgaris leucoagglutinin-immunoreactive terminals seemed to establish contact with non-cholinergic elements. Following Phaseolus vulgaris leucoagglutinin injection in the median raphe nucleus, very few labeled fibers with no evident close contact with nucleus basalis magnocellularis and substantia innominata cholinergic neurons were observed. After tryptophan hydroxylase/choline acetyltransferase double immunohistochemistry, a plexus of serotonergic (tryptophan hydroxylase-positive) fibers in the vicinity of choline acetyltransferase-immunoreactive neurons of the substantia innominata and nucleus basalis magnocellularis was observed, and some serotonergic terminals have been shown to come into very close contact with the cholinergic cells. Most of the tryptophan hydroxylase-immunoreactive terminals seem to establish contacts with non-cholinergic cells. Following FluoroGold injection in the nucleus basalis magnocellularis and substantia innominata, the majority of retrogradely labeled neurons was observed mainly in the ventromedial cell group of the dorsal raphe nucleus. In this area, a minority of the FluoroGold-positive neurons was tryptophan hydroxylase immunoreactive. These findings show that serotonergic terminals, identified in very close association with the cholinergic neurons in the substantia innominata and nucleus basalis magnocellularis, derive primarily from the B7 serotonergic cell group of the dorsal raphe nucleus, and provide the neuroanatomical evidence for a direct functional interaction between these two neurotransmitter systems in the basal forebrain.     

Selective anterograde tracing of nonserotonergic projections from dorsal raphe nucleus to the basal forebrain and extended amygdala

The dorsal raphe nucleus (DRN) contains both serotonergic and nonserotonergic projection neurons. Retrograde tracing studies have demonstrated that components of the basal forebrain and extended amygdala are targeted heavily by input from nonserotonergic DRN neurons. The object of this investigation was to examine the terminal distribution of nonserotonergic DRN projections in the basal forebrain and extended amygdala, using a technique that allows selective anterograde tracing of nonserotonergic DRN projections. To trace nonserotonergic DRN projections, animals were pretreated with nomifensine, desipramine and the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), 7 days prior to placing an iontophoretic injection of biotinylated dextran amine (BDA) into the DRN. In animals treated with 5,7-DHT, numerous nonserotonergic BDA-labeled fibers ascended to the basal forebrain in the medial forebrain bundle system. Some of these labeled fibers crossed through the lateral hypothalamus, bed nucleus of the stria terminalis, and substantial innominata. These fibers entered the amygdala through the ansa peduncularis and ramified within the central and basolateral amygdaloid nuclei. Other fibers entered the diagonal band of Broca and formed a dense plexus of labeled fibers in the dorsal half of the intermediate portion of the lateral septal nucleus and the septohippocampal nucleus. These findings demonstrate that the basal forebrain and extended amygdala receive a dense projection from nonserotonergic DRN neurons. Given that the basal forebrain plays a critical role in processes such as motivation, affect, and behavioral control, these findings support the hypothesis that nonserotonergic DRN projections may exert substantial modulatory control over emotional and motivational functions.     

Origin, distribution and morphology of serotonergic afferents to the mesencephalic trigeminal nucleus of the rat

We have studied the localization, the morphology and sources of serotonergic input on the primary afferent neurons in the mesencephalic trigeminal nucleus (Me5) of the rat with light and electronmicroscopy immunocytochemistry and with anterograde and retrograde neuroanatomical tract tracing methods. Me5 neurons were found to receive a serotonergic input that is part of a serotonergic fibre plexus extending over the neighbouring parabrachial nucleus and locus coeruleus. These serotonergic afferents originate predominantly from serotonergic cells in the dorsal raphe nucleus.     

通过猫脊髓背外侧索下行的单胺能神经元定位研究

将荧光染料核黄(NY)的逆行追踪和单胺荧光组织化学方法相结合,用于对通过猫脊髓背外侧索(DLF)下行纤维的胞体的定位。在4只猫上,于脊髓的T_2节段的DLF作单侧横切,并用NY处理以后,其脑干再用Falck和Hillarp的方法处理。在同侧的中缝大核和与之相毗邻的网状大细胞核内,看到被NY标记的5-羟色胺能神经元;在同侧上橄榄核的背外侧、蓝斑和蓝斑下核内,看到被NY标记的去甲肾上腺素神经元。这些结果暗示,DLF下行的单胺能纤维,主要起源于延髓的5-羟色胺能细胞群B_3和脑桥的去甲肾上腺素能细胞群A_5～A_7。     

犬心脏表面主要神经丛降钙素基因相关肽和P物质的免疫组织化学研究

目的 探明犬心脏表面神经丛的化学特性。方法 免疫组织化学ABC法。结果 在犬心脏表面各神经丛均见降钙素基因相关肽(CGRP)免疫反应阳性神经元，而SP免疫阳性神经元仅在心房背侧神经丛(DAP)、房间隔神经丛(IAP)和主动脉．肺动脉间神经丛(A—PP)内见到。CGRP—IR和SP—IR神经元形态、大小相似。心房表面神经丛内的CGRP—IR和SP—IR神经元都较心室表面神经丛者多。在心脏表面各脂肪垫及心肌间隙等处见到多量CGRP-IR、SP—IR神经纤维，多靠近血管或附于血管壁，在一些部位可见这两种肽能神经纤维似与心肌细胞接触。结论犬心脏表面神经丛内存在CGRP和SP；其在心脏内执行的功能可能有联系或相似之处，但也有不同；两种肽能神经对心房和心室的支配不对称，提示CGRP和SP可能直接参与心肌细胞和心脏血管活动的调控。     

The serotonin innervation of the cerebral cortex in the rat—an immunohistochemical analysis

The serotonergic innervation of the cerebral cortex in the rat has been studied by immunohistochemistry employing an antibody directed against the neurotransmitter, serotonin. The dorsal raphe, median raphe and B9 cell groups contain intensely labelled neuronal perikarya. Bundles of large diameter axons suggestive of fibers of passage are observed in successive sections as they ascend through the midbrain tegmentum, medial forebrain bundle, diagonal band and supracallosal stria en route to the cortex. In addition, a lateral pathway to the cerebral cortex traversing the ansa peduncularis is visualized. All regions of the cerebral cortex appear to be innervated by serotonergic axons which have a distinctive morphology: they are fine (0.1–0.5 μm), varicose, and extremely convoluted. Serotonergic axons of passage are thicker and comparatively straight. Throughout the lateral neocortex, as well as in the anterior cingulate cortex, serotonergic axons form a densely arborizing plexus through all cortical layers. Contrary to earlier reports, based on histofluorescence, describing a sparse innervation of the cortex with most of the fibers found in the molecular layer, the present study reveals that the innervation is relatively uniform across all cortical layers. In most of the cortex the density of serotonin-containing axons exceeds that of noradrenergic fibers. A distinctive and different pattern of serotonin innervation is found in the posterior cingulate cortex (cytoarchitectonic field RSg): the serotonergic axons are restricted largely to lamina I and III. A restricted laminar pattern also characterizes the innervation of the hippocampus; dense axonal plexuses occur in the outer rim of the dentate hilus and in the stratum lacunosum-moleculare. The serotonergic afferents to the cortex appear to have at least two different modes of distribution, a relatively uniform pattern in the anterior cingulate and the lateral neocortex and a restricted, laminar pattern in the posterior cingulate and the hippocampus.The density and extent of the serotonin innervation is such that the raphe neurons may contact every cell in the cortex. The widespread arborization of serotonin axons contrasts with the spatially restricted termination of thalamic afferents. The distribution of serotonin-containing fibers also differs substantially from the terminal patterns of noradrenergic and dopaminergic fibers. The differences in axonal morphology and distribution amongst the monoamine afferents reflect differences in their contributions to cortical circuitry. The present findings indicate that the serotonin-containing neurons may exert a profound and global, but not necessarily uniform, influence upon cortical function.     

Immunocytochemical localization of serotonergic fibers innervating the ocular circadian system of Aplysia

The isolated eye of the mollusc, Aplysia californica, contains a circadian pacemaker whose phase can be regulated by serotonin. The results of previous biochemical and physiological studies indicate that serotonin is used as a transmitter of circadian information in the eye. Although the effects of serotonin on various physiological processes in the Aplysia eye have been studied, very little is known about the anatomy of the serotonergic innervation. We have examined the innervation of the eye using immunocytochemical methods. Serotonin-immunoreactive processes were observed in the optic nerve, in the accessory optic nerves, in the connective tissue capsule surrounding the eye, and within the eye itself. There appeared to be two sources of serotonergic input to the eye of Aplysia. One set of immunoreactive fibers was contained in the optic nerve and entered the eye in the neuropil region before radiating outward towards the peripheral retina in the layer below the photoreceptor cell bodies. A second serotonin-immunoreactive input to the eye entered from the accessory optic nerves and these fibers formed a dense plexus of fibers in the connective tissue capsule surrounding the eye. Serotonin-immunoreactive fibers from the plexus penetrated the eye and appeared to terminate in the peripheral portion of the retina. No serotonin-immunoreactive cell bodies were observed in the eye, nerves, or connective tissue capsule. These results support the hypothesis that serotonergic fibers innervate the retina of Aplysia and that these fibers travel through two distinct anatomical pathways: the optic nerve and the accessory optic nerves.     

Non-serotonergic dorsal and median raphe projection onto parvalbumin- and calbindin-containing neurons in hippocampus and septum

The median raphe nucleus is involved in controlling and maintaining hippocampal activity through its projection to inhibitory neurons in medial septum and hippocampus. It has been shown that anterogradely axonal-traced fibers originating in the median raphe nucleus project onto calbindin-containing neurons in hippocampus and parvalbumin-containing neurons in medial septum. Parallel immunohistochemistry studies showing serotonin fibers contacting calbindin- and parvalbumin-positive neurons have led to the assumption that raphe fibers projecting on these types of neurons are mainly serotonergic. However, in both dorsal and median raphe nucleus there is a large amount of non-serotonergic neurons which also are projecting neurons, indicating that a part of the raphe fibers projecting to hippocampus and septum may be non-serotonergic. Our aim was to determine whether there is a non-serotonergic projection from the raphe nucleus onto calbindin- and parvalbumin-containing neurons in hippocampus and septum. Biotin dextran amine was used as the anterograde neuronal tracer and injected into either dorsal or median raphe nucleus. By use of triple immunofluorescence-labeling we analyzed the serotonergic content of the biotin dextran amine-labeled fibers contacting parvalbumin- and calbindin-positive neurons. Surprisingly, we found a significant non-serotonergic projection from both dorsal and median raphe nuclei onto calbindin- and parvalbumin-containing interneurons in septum and hippocampus, with a preference in hippocampus for projecting onto calbindin-positive neurons. These results indicate that the raphe nuclei may exert their control on hippocampal and septal activity not only through a serotonergic projection, but also through a significant non-serotonergic pathway.